The Guardian

WEATHER U: No rainbows - or snowbows - from winter snows

Sherry Beaman said the snow had just stopped when she spotted the faint rainbow. She wondered if it was indeed a snowbow? - Contributed

Last week after the warm air was pushed out by a cold front, flurries started to fall in the colder air: that’s when Sherry Beaman spotted this lovely rainbow.

She was surprised to see it because it was snowing at the time. Sherry wants to know if there is such a thing as a “snow bow.”

Not all rainbows are created equal. The most common rainbow is a true rainbow created when sunlight reflects and refracts off water droplets. It’s fairly common, but always nice to see.

Fog bows are also lurking out there. These are a little rarer – the light source has to be very low and behind you, plus the fog has to be just the right consistency. Too much or too little fog, and you won’t get one. Fog bows are also fainter than rainbows, sometimes appearing as a ghostly white.

Moonbows exist, too. If conditions are just right, rainbows can be produced by moonlight – which is, of course, reflected sunlight.

But snowflakes just don’t cut it. Snowflakes are often aggregates - collection of multiple snowflakes all clumped together as they fall from the sky. Light refracts off these in a more random way, so the wavelengths are not scattered out in an orderly fashion. Rainbows need spherical raindrops. Sunlight enters a drop, refraction changes the light’s direction, and it bounces off the sphere’s opposite side before leaving the drop.

There were flurries in the air when Sherry spotted her rainbow, but there also had to be some moisture in the air that had not yet frozen.